Weapon regeneration can promote unreliable signalling when reduced strength goes undetected

Abstract Animal weapons often signal fighting ability, and signalling theory predicts that weapon size should reliably reflect weapon performance. Weapon loss and regeneration can disrupt this relationship by decoupling signal magnitude from functional capacity, but the consequences of such mismatches should depend on whether opponents can detect regenerated structures and whether signal reliability is tested during contests. We tested these hypotheses in the crayfish Cherax destructor by experimentally removing one chela from 40 individuals and comparing weapon morphology, strength, growth, swimming performance and contest outcomes with 40 control individuals after 12 months of regeneration. Regenerated chelae were smaller, more slender and weaker for their size than original chelae, demonstrating a decoupling between weapon size and strength. Despite this reduction in performance, regeneration imposed few detectable costs on body growth or swimming performance. Contest experiments revealed that weapon size alone predicted success in interactions resolved by signalling, whereas both weapon size and strength predicted success when contests escalated to physical combat. Consequently, individuals bearing regenerated weapons gained the benefits of enlarged weapons during signalling interactions despite possessing inferior weapons during fights. Our findings are consistent with the expectation that unreliable signals can persist when opponents do not detect reduced performance and only occasionally test signal reliability through escalation. However, additional experiments are needed to isolate the sensory mechanisms underlying receiver assessment and to directly test detection of regenerated weapons. Read the free Plain Language Summary for this article on the Journal blog.